For that size, I'd take your ten yards of fabric and rip it into thirds from selvage to selvage. If you can get a couple of helpers, you can just fold it into thirds (in mid-air, kind of like when you get someone to help you fold a bedsheet). Then snip at the appropriate places and rip. Be sure to divide evenly - your ten yards divided into thirds gives you about five inches extra on each end of the quilt.
To assemble, I'd leave the selvages intact and line up the selvage of two pieces, right sides together. Take a very generous seam allowance that gets you past the selvage. I mark the seam allowance on my machine bed with painters tape. It will be a big amount, at least an inch, maybe more. (Don't overdo the allowance, though. You need almost the entire three widths of fabric for your back.) Do the same with the third piece. Then trim back to a normal seam allowance and press.